1. Field of the Invention
The present invention relates to tape cassettes and, more particularly, to tape reels around which a magnetic tape or the like is wound and a metal mold for manufacturing these tape reels.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings shows an example of a conventional tape reel. As shown in FIG. 1, the conventional tape reel comprises a reel hub 3 serving as a tape wrapping shaft and parallel upper and lower flanges 1 and 2 attached to the reel hub 3. These upper and lower flanges 1 and 2 restrict the positions of edge portions of a magnetic tape (not shown) wound around the reel hub 3 and the magnetic tape is wound around the reel hub 3.
When the above tape reel is made light-weight or is reduced in cost in accordance with the reduction of material, if the outer diameters of the upper and lower flanges 1 and 2 are the same, then it is proposed that the thicknesses of both surface sides of the upper flange 1 and the lower flange 2, i.e., the thickness of the upper surface side of the upper flange 1 and the thickness of the lower surface side of the lower flange 2 are reduced as shown in FIG. 1.
If, however, only the thicknesses of the front surface sides of the upper and lower flanges 1 and 2 are reduced, then the upper and lower flanges 1 and 2 are curved to the rear surface sides whose thicknesses are not reduced, i.e., the upper and lower flanges 1 and 2 are warped as shown by phantoms in FIG. 1. As a cause that the upper and lower flanges 1 and 2 are warped, it is considered that the upper and lower flanges 1 and 2 are warped because the upper and lower flanges are unevenly shrunk as the molded products are cooled after the tape reel was molded by the injection molding process.
Therefore, when the upper and lower flanges 1 and 2 are Warped toward the rear surface sides, a disc rotation fluctuation occurs while the tape reel is rotated. Further, the spacing between the upper and lower flanges 1 and 2 is reduced so that the edge portions of the magnetic tape wrapped around the reel hub 3 are pressed by the rear surfaces of the upper and lower flanges 1 and 2, which unavoidably damages a so-called tape edge.
To eliminate the aforesaid drawbacks, there has been proposed a tape reel 11 shown in FIGS. 2 and 3 of the accompanying drawings.
As shown in FIGS. 2 and 3, the front and rear flange surfaces are molded as three arcuate thin flanges portions 15 which result from reducing a uniform thickness from an outer peripheral edge portion 12 to a reel bearing shaft 13 while a plurality of (three) radial ribs 14 are left.
When the above tape reel 11 is molded by using a metal mold, as shown in FIG. 2, an amount of resin material flowed into the three arcuate thin flange portions 15 is small and the last injection of resin is effected on portions 15c of the outer peripheral sides of the flange portions 15. Consequently, air within a cavity of the metal mold and gas discharged from the molding material are not discharged to the outside of the cavity and remain within the cavity. As a result, a so-called short mold or weld line of the thin flange portion is produced in the molded product, which deteriorates the quality of the molded product. Also, the flange is warped due to the short mold and the rotation of the flange surface is fluctuated considerably. There is then the problem such that the edge portions of the magnetic tape wrapped around the tape reel are damaged.